1. Field of the Invention
The present invention relates to fluid-powered drilling motors useful for drilling oil wells and other subterranean bore holes
2. Background of the Invention
In drilling oil wells and other subterranean bore holes, the motive power to drive the drill bit on the tip of the drill string is normally provided by a fluid-powered drilling motor or xe2x80x9cmud motor.xe2x80x9d Conventional drilling motors are composed of two principle components, a stator housing or xe2x80x9cstatorxe2x80x9d and a rotating screw or impeller (hereinafter xe2x80x9crotorxe2x80x9d) located inside the stator. A fluid, typically drilling mud in the case of oil wells is pumped down the inside of the drill string at high pressure where it passes through the drilling motor between the stator and rotor to the outside the drill string. The rotor and stator are structured such that movement of fluid between them imparts a rotary motion to the rotor, this rotary motion being transferred to the drill bit for drilling the bore hole. See, for example, U.S. Pat. No. 3,878,903; U.S. Pat. No. 4,484,753; U.S. Pat. No. 5,195,754 and U.S. Pat. No. 5,956,995, the disclosures of which are incorporated herein by reference.
In order to direct the path of the bore hole, modern drilling equipment often includes a guidance system which senses the location of the drill bit and other parameters. Such systems typically include a sensor positioned in the drill string at or near the drill bit and a receiver located at the surface for receiving signals transmitted by the sensor. Based on the sensed location, various actions can be taken to direct, or redirect, the direction of the drill bit so that the bore hole produced achieves the desired location. This is especially important in directional well drilling where the path of the bore hole is changed at some preselected depth from vertically downward to laterally outward. See U.S. Pat. No. 5,467,832 and U.S. Pat. No. 5,448,227, the disclosures of which are also incorporated herein by reference.
Although the location of bore hole pathways can be controlled with reasonable accuracy using current technology, greater accuracy is still desired.
Accordingly, it is an object of the present invention to provide improved drilling equipment which allows the pathways of bore holes produced in subterranean formations to be controlled more accurately than currently possible.
This and other objects are accomplished by the present invention which is based on the discovery that greater accuracy can be achieved in sensing the underground location of drill bits and/or drilling motors during drilling of a subterranean bore hole if the drilling motor is made from non-magnetic components which are substantially iron-free. In particular, it has been determined in accordance with the present invention that the inability of current guidance systems to sense the location of underground drill bits with high accuracy is due at least in part to magnetic interference caused by the drilling motor or its components. Although non-magnetic alloys are typically used for making the rotors and stators of many drilling motors, over time these alloys can develop localized areas or regions of significant magnetism. These areas of magnetism, in turn, interfere with the signals transmitted by the sensor of the guidance systems to indicate drill bit location. In accordance with the present invention, therefore, the drilling motor is formed from alloys which are not only non-magnetic but also substantially iron-free as well. As a result, the tendency of the drilling motor to develop areas of magnetism over use is largely eliminated.
Thus, the present invention provides an improved drilling motor for use in drilling subterranean bore holes in which the significant components of the drilling motor are formed from alloys which are not only non-magnetic but also contain less than 0.1 weight percent iron. Preferably, the drilling motor is made from components such that the drilling motor, as a whole, contains less than 0.1 weight percent iron, based on the entire weight of the drilling motor.